Hello,
thanks so much Nick.
I completly agree with you, and i stoped really quickly to run without vcc yesterday.
I need to use your advices for my scketch but I think having found the gulty...
With Vcc=5V all captors run correctly. At the beginning I decided to use the better voltage for the MLP115A1 and the SHT15. 3,3V was the better level to reduce the consuption. But now, when I control the voltage, I find 4,3V!!! and it's also the same voltage on the SD-shield and the Arduino Board. I know that 3,3V is using by the SD-card, and in fact I have some regularly problems to establish the communication with the card...
In brief, in think the regulator 3,3V on the Arduino board is defective... that can explain all events...
What do you think about my supposition? I have also some doubts about the SD-shield...
Have a good weekend.